|Publication number||US7690324 B1|
|Application number||US 11/200,338|
|Publication date||Apr 6, 2010|
|Filing date||Aug 9, 2005|
|Priority date||Jun 28, 2002|
|Publication number||11200338, 200338, US 7690324 B1, US 7690324B1, US-B1-7690324, US7690324 B1, US7690324B1|
|Inventors||Jingbin Feng, Steven T. Mayer, Daniel Mark Dinneen, Edmund B. Minshall, Christopher M. Bartlett, Eric G. Webb, R. Marshall Stowell, Mark T. Winslow, Avishai Kepten, Norman D. Kaplan, Richard K. Lyons, John B. Alexy|
|Original Assignee||Novellus Systems, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (18), Referenced by (12), Classifications (11), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a continuation-in-part application, claiming priority under 35 USC 120, of co-owned and co-pending U.S. patent application Ser. No. 10/609,518, filed Jun. 30, 2003, by Mayer et al., having the title “Liquid Treatment Using Thin Liquid Layer”, which claimed the benefit of U.S. Provisional Application Ser. No. 60/392,203, filed Jun. 28, 2002, and which is incorporated herein by reference for all purposes.
The invention is related to the field of integrated circuit fabrication, in particular to methods and apparatuses for the electroless deposition of metal thin films using liquid chemical reactions.
Electroless plating (or electroless deposition) of copper and other metals has received increasing interest in recent years. This interest is due in part because of the relatively low cost of electroless processes compared to other (e.g., vacuum) deposition techniques, and because of generally surface-controlled, selective, conformal deposition properties of electroless processes. Electroless deposition has a number of potential applications, such as repair of marginal seed layers for copper damascene electroplating, creation of seed layers and barrier layers directly on dielectrics that can be plated, and selective deposition of barrier and electromigration capping layers onto damascene metal (e.g., cobalt and cobalt alloys on copper).
Conventional electroless metal deposition is conducted in a system containing one or multiple open baths containing plating solution. In a typical operation, a wafer holder immerses a substrate wafer face down in the plating solution during plating operations. The plating solution is exposed to ambient air, especially when the substrate wafer is being moved and the wafer holder does not cover the plating bath surface. Thus, an open bath system has disadvantages. For example, during the metal deposition step, ambient oxygen is readily dissolved in the solution, and the dissolved oxygen can interfere with the desired metal deposition (e.g., by slowing or preventing metal deposition). Electroless plating operations are performed at elevated temperatures in a range of 40° C. to 90° C., typically in a range of about 50° C. to 80° C. At these temperatures, the plating solution components have a tendency to evaporate. The tendency of water and volatile components to evaporate is exacerbated by the need to ventilate the gaseous spaces over a plating bath, especially to remove explosive or toxic fumes inherent to the electroless solution (e.g., ammonia gas) or created by spontaneous decomposition of its components (e.g., dimethylamine, hydrogen). The heating load caused by evaporation substantially increases the size and costs of a heater required to maintain plating bath temperature. Condensation of evaporated bath constituents on plating-cell walls and on the wafer holder are a source of backside contamination. Subsequent crystallization of those same condensates causes other contamination problems. Maintaining bath concentration, therefore, requires complicated and expensive monitoring and control techniques. See, for example, U.S. Pat. No. 6,537,416, issued Mar. 25, 2003 to Mayer et al., and U.S. Pat. No. 6,713,122, issued Mar. 30, 2004, to Mayer et al., which are hereby incorporated by reference. A conventional electroless plating bath typically can have a bath volume of 20 liters or more. Typical bath turnover rates required to avoid plate-out and composition drift are 6 hours to 10 hours. Assuming a processing rate of 20 wafers per hour, approximately 160 wafers can be processed with 20 liters.
A problem of both face-down and face-up plating configurations is hydrogen-bubble entrapment on the plating surface and resulting defects. Hydrogen gas is created as a byproduct of almost all known electroless plating-solution reducing agents. A byproduct of most electroless plating oxidation half-reactions (i.e., the oxidation of the reducing agent) and of the self-degradation of the reducing agents is dissolved molecular hydrogen (H2). As these reactions continue (i.e., plating reactions and bath-aging), the amount of hydrogen increases until the solution becomes saturated and eventually supersaturated with dissolved hydrogen. When this occurs, the formation of hydrogen gas (bubbles) is spontaneous, and occurs most readily on solid interfaces (e.g., vessel walls, wafer surfaces). Areas in which bubbles are attached to the wafer are not plated, creating defects. Therefore, it is advantageous to utilize designs that minimize the propensity for hydrogen formation, or minimize the effective bath age. United States Patent Application Publication No. 2003/0141018, by Stevens et al., published Jul. 31, 2003, teaches an electroless deposition apparatus in which a substrate support holds a substrate wafer in a face-up orientation to reduce bubble-formation and an evaporation shield is positioned over the substrate to form a gap that is filled with liquid plating solution.
Solution pH influences the reaction rate of the electroless plating process. It is often useful to utilize an alkaline pH-adjuster, for example, lithium-, sodium-, or potassium-hydroxide, but preferably ammonium- or tetramethylammonium hydroxide (“TMAH”) to maintain or adjust the pH. Alkali metal pH-adjusters are inexpensive, but are often unsuitable for semiconductor applications because of their rapid diffusion into and poisoning of various device materials. Ammonium hydroxide is also inexpensive and does not generally degrade device performance, but it is volatile. Therefore, the maintenance of ammonium hydroxide concentration in a plating bath is problematic. TMAH and other analogous organic cation hydroxides do not suffer from either of these problems, but are significantly more expensive. The constituents of a semiconductor electroless plating solution, particularly the reducing agents and TMAH, can be expensive, leading to bath costs in a range of $25/liter to $100/liter. Therefore, one would like to use lower cost materials without the negative impacts. Also, the waste treatment of electroless plating solutions is complicated and expensive. A waste treatment process generally involves forced decomposition of the reducing agents, accompanied by hydrogen gas stripping and dilution. A small amount of dissolved reducing agent can spontaneously breakdown to create a large volume of hydrogen gas in a storage container (an explosive hazard), so the removal of reducing agents must be driven to completion. A plating solution must also be stripped of metal. The cost of such plating solution post-processing (including capital equipment costs) is typically in a range of $5/liter to $10/liter. Inefficient use of the plating solution, therefore, increases the cost of plating operations significantly.
Electroless plating solutions are also often inherently unstable. The instability manifests itself in auto-degradation of bath constituents and in the “plating-out” of bath metal as fine metallic particulate in the bulk solution and onto processing equipment walls, filters, and other system components. The presence of plate-out particles also increases the number of defects in the workpieces and diminishes process yield. Generally, the instability of plating solutions increases with reducing agent concentration and with temperature, and decreases with the addition of bath “stabilizers” (e.g., oxygen, chlorine, lead, tin, cadmium, selenium, tellurium). In opposition to this trend, the initiation of electroless plating of a particular metal onto a substrate and the plating deposition rate are also proportional to reducing agent concentration and temperature, and decrease with the addition of bath stabilizers. Thus, plating-solution instability and electroless plating rate and nucleation are inherently linked in a non-advantageous manner.
Spray techniques have been suggested for electroless plating. See, for example, U.S. Pat. No. 6,065,424, issued May 23, 2000 to Shacham-Diamand et al. In such techniques, reacting plating solution is applied to a wafer surface as a spray or mist. Typically, the wafer is rotating under the spray or mist, and liquid solution is spun radially outwards. Under such conditions, it is difficult to maintain a sufficiently high and uniform reaction temperature because of the simultaneous cooling of the hot fluid by evaporation of the solvent (e.g., water). Alternatively, heating the backside of the wafer by a heated chuck is possible. Nevertheless, this requires a relatively massive element with sufficient heat capacity to maintain a globally uniform temperature over a standard 200 millimeter (mm) or 300 mm wafer. Also, the face-up base of the heating element/chuck is susceptible to chemical contamination and transfer of that contamination to the wafer backside. Furthermore, backside heating does not solve the problem of non-uniform evaporation and cooling of the bath solvent.
A wafer chuck should be capable of spinning at high revolutions per minute (rpm) to enable spin-drying. Splashing of liquid against apparatus walls and misting back onto the product surface can cause contamination of the apparatus and defects on the workpiece. Evaporation and misting of plating solution into the plating space results in substantial loss of the plating solution, and unwanted formation of volatile hazardous chemicals in the effluent.
Wet processing of isolated conductive-metal circuits connected to transistor elements in the presence of light and electrolyte often encounters a number of processing challenges. One problem is the creation of a photo-induced power source when p-n junctions in the base-circuit transistors are exposed to light. Another problem is the completion of a corrosion circuit on the surface being processed between the exposed isolated metal lines and a processing electrolytic solution. The energy of the light photons is converted to electrical energy, creating a reverse bias potential and a corrosion circuit.
Thus, liquid chemical reaction techniques, for example, immersion bath and spraying techniques, typically encounter problems such as: difficult or unsuitable control of reaction and process conditions; inability rapidly or dynamically to vary various operating conditions; inability to handle unstable reaction mixtures; accumulation of reaction byproducts; inefficient use of expensive liquid solutions; frequent wafer-handling between process steps; high capital cost of equipment for multi-step processes; and excessive use of valuable clean-room floor space.
The invention helps to solve some of the problems mentioned above by providing systems and methods for fluid treatment, particularly liquid treatment, of integrated circuit substrates using a thin fluid layer in a small volume of fluid.
A novel small-fluid-volume processing apparatus enables processing of integrated circuit wafers with high throughput and low cost of ownership. Embodiments of such an apparatus are useful for, among others: selective electroless plating of cobalt and nickel (including combinations of Co, Ni, B, P, and W using electroless process solutions); nonselective electroless plating (e.g., deposition of seed layers or the modification of vacuum-deposited seed layers by electroless copper deposition); metal etching (e.g., etching of copper, Ta, TiSN, Co, Ni, etc.); electroless (chemical) polishing (e.g., of copper); various surface treatments (e.g., copper surface reaction with benzotriazole or 3-mercapto-1-propane sulfonic acid); and cleaning and rinsing operations. In particular embodiments in accordance with the invention, a cobalt alloy is electrolessly plated onto copper material in an integrated circuit substrate. An example is a cobalt-capping layer for capping copper.
The invention is described primarily with respect to its application to electroless plating, but the invention also includes embodiments useful for other treatments of a substrate wafer surface using a small volume of fluid enclosed in a treatment space, particularly chemical liquid reaction processes and related pretreatment and post-treatment operations. For example, removal of metal layers is also conducted in accordance with the current invention.
Embodiments in accordance with the invention enable efficient use of small volumes of often unstable fluid reactants and other processing chemicals at elevated temperatures, with preferred embodiments having the ability to recycle these chemicals to reduce operating costs further.
Embodiments in accordance with the invention also provide efficient use of surface-cleaning and particle-removing chemicals and the use of minimal water for rinsing operations. Electroless (or chemical) plating, polishing, etching, and rinsing operations are conducted in accordance with the invention with a high degree of global uniformity, using a minimal amount of fluid reactant.
A small volume of treatment fluid (e.g., electroless plating solution) in accordance with the invention is enclosed in a small-volume treatment space located in a microcell container and is in fluidic contact with a treatment surface of a wafer substrate. In this specification, therefore, a small fluid-treatment volume for performing a liquid treatment of a substrate surface, or a container in which a small fluid-treatment volume is located, is sometimes referred to as a “microcell”. The terms “microcell”, “microcell technology”, “microcell module”, and related terms are also used to refer to an apparatus or method in accordance with the invention comprising a small-volume treatment fluid contained in an enclosed space of a microcell container. Typically, a treating liquid is injected into a microcell container and then a substrate carrier supporting a substrate wafer is lowered into the container to form a small fluid-treatment volume filled with liquid, though this sequence may obviously be reversed as well.
In one aspect of the invention, a small fluid-treatment volume provides control of the degree or extent of the particular treatment operation. For example, by inserting a certain volume of liquid reactant at a certain concentration at a controlled temperature into a microcell container and allowing it to remain in the container in contact with a substrate wafer for a time sufficient for a known reaction to run to completion or to an equilibrium point, a controlled known amount of material is deposited on the substrate. For example, a layer having a thickness of 50 nanometers (nm) is deposited by including a known number of moles of reactants in the small fluid-treatment volume sufficient to deposit 50 nm of material, and no more. Similarly, in an etching operation, a desired thickness of material is removed from a substrate surface by including a known number of moles of reactants in the small fluid-treatment volume and allowing them to react to completion.
In another aspect, such measured deposition, etching, or other treatment operations are conducted in a series of steps. For example, a partial electroless plating of metal is conducted, the substrate's treatment surface is examined, and then a further operation is conducted to complete metal deposition. In another aspect, a treatment is conducted in a series of steps because a single-step operation is undesirable or impossible because of the production of reaction byproducts or for other reasons. For example, in the electroless plating of cobalt on copper, oxidation of the reducing agent generates hydrogen gas. In some embodiments, since the liquid in the small fluid-treatment volume has a limited solubility of hydrogen gas, the liquid is flushed from the fluid gap and replaced with fresh reactants.
Another advantage of an apparatus and a method in accordance with the invention is that the composition of a treatment fluid and the flowrate of a treatment fluid into an enclosed treatment space of a microcell container is controllable and dynamically variable during treatment operations. In one aspect, certain processes of a substrate treatment, such as nucleation, are conducted under quiescent conditions by injecting a certain volume of reactant liquid at a particular concentration into a microcell container and allowing it to sit. In contrast, in certain other processes of some embodiments, such as in a growth phase of electroless cobalt plating, liquid reactant is continuously flowed into the treating space, generating convection in the small fluid-treatment volume.
A microcell apparatus in accordance with the invention is suitable for solving various problems related to electroless plating. In electroless plating techniques, some chemical reactant solutions are chemically unstable. In conventional plating technology, which usually relies on a bath, multiple liters of reactant liquids and other processing liquids are used. When they are unstable and they degrade, they can no longer be used. In a microcell in accordance with the invention, very small amounts of liquid are used per wafer substrate treated. A conventional immersion bath typically holds a volume of 15 liters to 20 liters. In contrast, the volume of a small fluid-treatment volume in accordance with the invention is generally in a range of about from 10 milliliters (ml) to 3500 ml, typically 25 ml to 2000 ml, and more typically 100 ml to 500 ml, depending on wafer size, process gap height, and hardware geometry.
Electroless plating involves a chemical reduction-oxidation (redox) reaction of dissolved metal ions in solution to achieve the desired metal deposition on a substrate. The chemical reaction is typically sensitive to temperature and to pH. A carrier/wafer assembly positioned proximate to the inside bottom surface of a microcell container forms a thin enclosed treatment space having a small volume. The small-volume treatment space is filled with liquid reactants or other fluid, depending on the phase of the process. The resulting small fluid-treatment volume allows temperature and pH, as well as other process variables, to be controlled and varied effectively. Among other functions, the bottom and/or sidewalls of the microcell container serve as a pre-heated “thermal mass”, or “heat capacitor”, that heats or cools the treatment fluid and maintains it at a desired temperature. By changing the temperature of a microcell container, the temperature of the small volume of treatment fluid is changed to a new temperature.
Embodiments in accordance with the invention also enable electroless plating in a dark environment.
In another aspect, pre-treatment, liquid chemical treatment, and post-treatment operations are conducted in the same module, or “supercell”. In another related aspect, a supercell in accordance with the invention comprises a plurality of microcell containers and substrate carriers for performing multiple operations in a single microcell module.
In one aspect, a single tube or a plurality of tubes function as liquid inlet tubes into the microcell container. Typically, an inlet tube defines an inlet port located at the periphery of microcell container so that fluid is injected proximate to the periphery of the treatment space. In some embodiments, liquid treating fluid (e.g., electroless plating solution) is injected into a microcell container tilted at an angle, and then the carrier/wafer assembly is gradually lowered to form a fluid-filled enclosed treatment space. Accordingly, a leading edge of the substrate wafer penetrates the liquid surface and a liquid wetting front moves across the wafer surface as the wafer is lowered further into the microcell container until a substantially enclosed treatment space between the substrate wafer and the bottom of the container is completely filled with liquid. This alternative is useful in avoiding the formation of trapped air pockets or bubbles within a small fluid-treatment volume. Alternatively, a carrier/wafer assembly is lowered into a microcell container to form a small-volume enclosed treatment space, and then treating fluid (typically liquid) is injected through one or more inlet ports to form a small, enclosed volume of treating fluid in contact with the treatment surface of the substrate. In preferred embodiments, an apparatus includes a seal between the carrier/wafer assembly and the sidewall of the microcell container when the carrier/wafer assembly is in a lower, “treating” position forming the enclosed treatment space. An apparatus in accordance with the invention preferably includes one or more exhaust ports for venting fluid (e.g., air) as a carrier/wafer assembly is lowered into treating fluid, or as treating fluid is injected into an enclosed treatment space.
Cobalt and some other metals are magnetic. In one aspect of the invention, magnetic force is used to attract magnetic particles of cobalt (or other metal) and thereby remove cobalt-containing particulate matter from a chemical reactant liquid, from a liquid layer, or from the surfaces of a microcell apparatus. In another aspect, a magnetic field is formed in a microcell to control and focus deposition of cobalt (or other metal) onto a treatment surface. Thus, an electromagnet in a wall of the microcell container or in the substrate holder is used to enhance nucleation, growth, and selectivity. In still another aspect, the magnetic field created by cobalt deposited on a treatment surface (or other magnetic material on a substrate) is measured to determine the amount of material deposited, the thickness of the layer, thickness uniformity, and topography. This allows efficient endpoint determination. In another aspect, continuous measurement of magnetic fields created by deposited cobalt or other magnetic material enables real-time feedback and quality control.
In still another aspect, light is shown into the thin enclosed treatment space and an optical sensor measures reflectivity, spectra, or some other optical property to measure layer thickness, layer uniformity, and/or topography.
In another aspect, a thin enclosed treatment space in accordance with the invention comprises a gap, the gap typically having a gap height in a range of about from 1 mm to 5 cm and a gap volume in a range of about from 0.1 cm3 per cm2 of wafer treatment surface to about 5 cm3 per cm2 of wafer treatment surface.
An apparatus in accordance with the invention is useful for electrochemical treatments of a substrate surface, such as electroplating and electropolishing, by electrically biasing the microcell container and establishing an opposite bias on the substrate surface.
Other features, characteristics and advantages of embodiments in accordance with the invention will become apparent in the detailed description below.
A more complete understanding of the invention may be obtained by reference to the drawings, in which:
The invention is described herein with reference to
The terms “fluid treatment”, “treatment”, and related terms are used in a broad sense in this specification to designate any treatment of an integrated circuit substrate using liquid and/or gas phases, including, for example, pre-treatment operations, cleaning techniques, liquid chemical reactions, rinsing, drying, and post-treatment operations. The term “liquid chemical reaction treatment” is also used in a narrower sense and refers to a treatment conducted at the treatment surface of an integrated circuit substrate involving chemical reaction; for example, deposition, etching, and polishing operations. Broad categories of chemical liquid reaction treatments include electroless metal plating, electroless etching, electrolytic plating, electrolytic etching, metal-oxide deposition, and liquid dielectric deposition.
The term “dynamically variable” and related terms means that a variable or parameter of an apparatus, method, or composition is variable during a treatment process.
In another aspect, a microcell container is heated and maintained at an elevated temperature by one or a plurality of means. In some embodiments, an electrical heating element is embedded into walls of a microcell container. The temperature is controlled by a regulator that senses the container's temperature via thermocouple, thermistor, or similar device embedded in the bulk of a container wall. Alternatively, a heat exchange manifold with a high-surface-area fluid path interfaces with flow of an externally temperature-controlled head-exchange fluid.
Microcell container 105 comprises a significant mass of a highly conducting material with a heat capacity substantially greater than that of a substrate wafer. Generally, the total (not specific) heat capacity of the microcell container is designed to be more than 10 times greater than that of a substrate, and the thermal conductivity of the heating mass in the container walls is designed to be high, generally greater than 0.2 Watt cm−1 K−1. Examples of suitable head container materials are metals such as Copper (Cu), Aluminum (Al), Titanium, stainless steel, and Iron, particularly Aluminum and Copper.
An exemplary microcell container has a bottom wall thickness and a sidewall thickness of 2.5 cm. A microcell container typically is designed to treat a substrate wafer having a particular diameter. The container space of a microcell container usually is designed to have an inside diameter about 3 cm greater than the diameter of a wafer to be treated. The container space 214 of an exemplary microcell container designed to treat a 300 mm wafer has an inside diameter of about 33 cm and an inside sidewall height of 8 cm. Accordingly, the inside diameter of a sidewall 206 of an exemplary microcell container designed to treat a 300 mm wafer has an inside diameter of about 33 cm
In a typical electroless process, over time the plating metal tends to plate onto any available metal surface. The ease of initiation of the plating depends on a number of variables, including roughness, surface oxides, metal catalytic reactivity with the reducing agent, and metal ion reduction charge-transfer resistances. Therefore, the presence of exposed metal surfaces in a microcell container or of a substrate carrier is potentially problematic. Nevertheless, it is generally desirable to use metal because metals provide high thermal conductivity. Therefore, to avoid undesired plating of plating metal onto a metal surface of a microcell apparatus, in certain embodiments the exposed surfaces of a container, substrate carrier and other elements are covered with a plastic film. Typically, the plastic film has a thickness of about 1 mm or less to minimize interference with heat exchange between the microcell-container walls and the small fluid-treatment volume. As depicted in
In one aspect, pre-wetting and cleaning of the treatment surface is conducted before plating or other chemical liquid reaction treatment. For example, exposing the treatment surface with an activator solution prior to nucleation is conducted using a small fluid-treatment volume in the fluid gap, or alternatively by spraying or otherwise rinsing the treatment surface.
In this specification, terms of orientation, such as “face-down”, “above”, “below”, “up”, “down”, “top”, “bottom”, and “vertical” used to describe embodiments relate to the relative directions in FIGS. 1 and 7-12 in which a horizontal base plate 132 defines a substantially horizontal plane. It is understood, however, that the spatial orientation of substrates and apparatuses in embodiments in accordance with the invention are not confined to those depicted in the drawings.
The term “enclosed treatment space” and related terms is used broadly to designate a treatment space in a container that is substantially enclosed. For example, in preferred embodiments, a carrier/wafer assembly creates a seal with the sidewalls of microcell container. In other embodiments, a fluid-tight seal is not established, but the carrier/wafer assembly effectively inhibits evaporation or other undesired escape of liquid present in the treatment space.
The term “face-down” and related terms generally refers to the orientation of a treatment surface of a substrate wafer relative to a horizontal plane. In a narrow sense, face-down means that the treatment surface of a wafer is horizontal and facing vertically downwards. Because embodiments in accordance with the invention enable tilting a microcell container and a substrate carrier, the terms “face-down”, “substantially face-down” and related terms mean that a line perpendicular to a treatment surface of the wafer makes an angle less than 90° relative to the vertically downwards direction, generally less than 45°, and preferably less than 20° relative to vertical.
The term “inject fluid” and related terms used with respect to flowing a fluid such as an electroless plating solution into a thin enclosed treatment space in this specification are used broadly to refer to several different types of fluid-flowing operations. In one sense, flowing liquid or gas into a microcell container means simply injecting fluid into the container. Then, after a small fluid-treatment volume has been formed, the flow of liquid into the thin fluid gap ceases. Alternatively, fluid continues flowing at the same flow rate or continues at a different flow rate. In a second sense, therefore, flowing liquid into a thin fluid gap means continuously flowing liquid, either at steady-state or at an unsteady state, into a thin enclosed space and out of the space at a corresponding flow rate. It is a feature of some embodiments in accordance with the invention that a fluid treatment can be conducted by injecting fluid into a container and forming a small fluid-treatment volume, and then ceasing flow for a period of time, thereby conducting essentially a batch operation. On the other hand, continuous flow operations are conducted in some embodiments.
Processes 510 include loading a substrate wafer into a substrate carrier such as substrate carrier 108 in a load position, as depicted in
Processes 520 include using tilt actuator 130 to moved tilt table 124 from a horizontal orientation to an angled (tilted) orientation, typically to an angle in a range of about from 5° to 15°, as depicted in
Optional processes 530 include moving carrier/wafer assembly 410 into a position corresponding to the rinse position depicted in
Processes 540 include injecting treating liquid 422, such as electroless plating solution, into microcell container 105, as depicted in
Processes 550 include moving carrier/wafer assembly 410 towards a treating position, as depicted in
In processes 555, liquid treating operations proceed in thin enclosed treatment space 442 (
In processes 560, after liquid treatment, carrier/wafer assembly 410 generally is moved upwards to a rinse position, as depicted in
Processes 570 include moving carrier/wafer assembly 410 upwards to the load/unload position, as depicted in
In processes 580, carrier/wafer assembly 410 and other elements of apparatus 102 are moved from a tilted orientation back to horizontal for unloading and re-loading a substrate wafer.
It is understood that processes 510-580 can be conducted in sequences different from the order presented here. For example, in some embodiments, processes 520 of tilting apparatus 102 are conducted after processes 540 of injecting treating liquid into the microcell container. It is also understood that processes 510-580 may be conducted with the exclusion of selected steps or inclusion of extra steps; for example, microcell container 105 may be rinsed between subsequent wafers by refilling with a rinse chemical, such as deionized water.
During electroless plating of cobalt, the pH often tends to drift. For example, in some embodiments, a liquid plating solution contains an ammonium ion and the solution is heated to an elevated temperature. In aqueous solutions, the ammonium ion is in equilibrium with the amount of dissolved ammonia gas by the chemical equilibrium:
NH4 ++OH−←→NH3(dissolved gas)+H2O.
Since warm dissolved ammonia gas has a relatively high partial vapor pressure, it tends to evaporate very quickly into any air above the bath. Continual or continuous adjustment of pH and other liquid properties is done with a multiple chemistry flow capability by which chemical constituents of a reactant solution are contained in a plurality of reactant liquid sources, and the flow rate from one or a plurality of liquid sources into the thin enclosed treatment space is dynamically variable.
In another aspect, the chemical composition of a plating solution is varied during plating operations so that the chemical composition of the deposited metal layer varies spatially within the layer. Such a structure may alternatively be viewed as a multilayer structure. For example, phosphor, tungsten, or boron are known to improve the barrier properties of cobalt. In accordance with certain aspects of the invention, a particular cobalt alloy is deposited at the bottom of a capping layer, a different cobalt alloy is formed for the bulk of the capping layer, and a third cobalt alloy provides the top of a capping layer.
In still another aspect, modules comprising microcell (small fluid-treatment volume) devices in accordance with the invention are stacked substantially vertically. This enables higher throughput of substrates per unit surface area of manufacturing floor space. Since pre-treating, rinsing, and post-treating operations are performed in a single or in a plurality of microcells in accordance with the invention, utilization of production space improves.
Although embodiments in accordance with the invention are described herein mainly with respect to electroless plating techniques, it is clear that apparati and methods in accordance with the invention are useful for many types of wet substrate treatments. Various substrate treatments include liquid chemical reactions as well as non-reactive treatments (e.g., pre-treatment cleaning and rinsing). In an important aspect of the invention, a plurality of substrate treatments of a substrate are conducted sequentially in one module or supercell. An example of a liquid chemical reaction treatment is the uniform etching of a substrate surface. Another example is the stripping of an oxide from a substrate surface. For example, a protective oxide layer or an oxide layer that simply formed in an oxidizing environment is stripped off before electroless plating operations begin. In another aspect, metal particles and other contaminants are cleaned from a substrate carrier, inside container walls, and other surfaces prior to liquid chemical reaction treatment. An advantage of using a microcell or supercell apparatus in accordance with the invention is that the process conditions are closely controlled and dynamically variable. Similarly, the composition of the liquid plating solution is dynamically variable. Another advantage is that many or all of the pretreatment, rinsing, drying and other process operations are conducted in a supercell in accordance with the invention.
Electroless plating is an autocatalytic plating technique. The process physics enable selective deposition of a metallic coating by a controlled chemical reduction that is catalyzed on the metal or alloy being deposited. Electroless plating depends on the action of a chemical reducing agent in solution to reduce metallic ions to the metal. Unlike a homogeneous chemical reduction, the plating reaction takes place only on “catalytic” surfaces rather than throughout the plating solution. The process occurs by the simultaneous reduction of metal and the oxidation of a “reducing agent” on the metal surface. These two processes do not have to occur at exactly the same place on the metal surface, but there must be an electrical path between the location of the reducing agent's oxidation (generating excess electrons) and the location of metal deposition (combining the generated electrons with metal ions). Electroless plating has been used for depositing a large number of materials, including Cu, Ni, Co, Fe, Pd, Pt, Ru, Rh, Au, Ag, Sn, Pb, as well as alloys containing these metals, plus Mn, Mg, W, P and/or B. Various metals are deposited electrolessly onto an electronic component, including, for example, copper, nickel, cobalt, gold, silver, palladium, platinum, rhodium, cobalt, tungsten phosphorous, and combinations thereof. Electroless polymerization is performed by an analogous electroless process for some conductive polymers (e.g., polyanaline). Typical chemical reducing agents include ammonium hypophosphite ((NH4)H2PO2), formaldehyde (CH2O), hydrazine, borohydride, dimethylamine borane (DMAB), glyoxylic acid, redox-pairs (e.g., Fe(II)/Fe(III)) and derivatives of these. A chemical reducing agent in plating solution is a source of electrons for the reduction of a metal ion to a deposited metal atom on the surface:
M n+ +ne=M 0
where Mn+ represents a reducible metal ion in the solvent (typically water). Complexing agents (e.g., acetate, succinate, malate, malonate, citrate, etc.) are often used in plating solutions to enhance solubility at pH values where the metal ion would otherwise be insoluble. Complexation of the metal is also useful for shifting the potential of deposition to obtain desirable conditions for deposition.
In some cases, a particularly strong and catalytically-active reducing agent is important at the beginning of an electroless plating process in order to initiate plating of the metal onto the substrate surface. This is even more important in cases where the initiation of the plating process is on a foreign metal surface (e.g., initiation of cobalt electroless deposition onto a copper surface).
Accordingly, some embodiments in accordance with the invention involving electroless plating on a foreign substrate (e.g., cobalt on copper) comprise a two-phase process including a nucleation phase and a growth phase. In the nucleation phase, a desired depositing metal (e.g., cobalt) is caused to deposit on a foreign metal substrate surface (e.g., copper). Afterwards, in the growth phase, the desired metal (e.g., cobalt) grows on a film of similar metal (e.g., cobalt). Typically, optimum or idealized process conditions for the nucleation phase are different from those of the growth phase. For example, for electroless plating of cobalt on copper, the optimal set of conditions for the nucleation reaction to occur is very different from that of the growth reaction. Nucleation of cobalt onto a copper substrate involves the generation of excess reduced cobalt-metal atoms at the copper surface at a sufficient concentration for formation of a nucleation layer of cobalt. To create this concentration of surface cobalt atoms, a reducing agent of sufficient strength (i.e., an agent having suitable free-energy driving-force and kinetics) to reduce sufficient metal ions at a sufficiently rapid rate is required. One example of such a reducing agent is mopholine borane. Because the process of cobalt-ion reduction is likely stepwise, the creation of partially-reduced surface-absorbed metal ions presents a problem. The partially-reduced ions can diffuse away into the electrolyte and not aid in the nucleation process. To minimize this possibility, initiation of the electroless plating operation during a nucleation phase is typically performed under stagnant conditions. If the wafer were spinning quickly, rapid vigorous fluid flow would prevent the partially-reduced cobalt ions from accumulating, and nucleation would slow or not occur. On the other hand, once nucleation has occurred, the kinetics of the reducing-agent oxidation and cobalt reduction are quite different. It is believed that cobalt grows on cobalt in a more rapid, virtually single-step reduction reaction, and fluid convection caused by a high rotational speed enhances mass transfer and deposition rates. Furthermore, the kinetics of the reducing agent (e.g., morpholine borane) are substantially slower on the cobalt surface than on copper. Therefore, during the cobalt growth phase, a different set of chemical (composition and concentration of reducing agents) and physical (e.g., temperature, rotation rate) conditions are desirable.
Thus, in one aspect of the invention, a method for electroless plating of a cobalt alloy on copper comprises two distinct process phases, nucleation and growth, which are conducted separately under different process conditions, usually with different process chemistry. Typically, a third phase, activation, precedes nucleation. Co-owned and copending U.S. patent application Ser. No. 10/609,518, filed Jun. 30, 2003, by Mayer et al., which has been incorporated by reference, teaches a generalized method for conducting electroless deposition of cobalt using three distinct process phases in a thin-liquid-layer reactor. The teachings of U.S. application Ser. No. 10/609,518 are adaptable to methods and apparati in accordance with the present invention.
The particular systems, designs, methods and compositions described herein are intended to illustrate the functionality and versatility of the invention, but should not be construed to be limited to those particular embodiments. Systems and methods in accordance with the invention are useful in a wide variety of circumstances and applications to conduct a liquid chemical reaction treatment and other liquid-phase and gas-phase treatments performed on an integrated circuit substrate. It is evident that those skilled in the art may now make numerous uses and modifications of the specific embodiments described, without departing from the inventive concepts. It is also evident that the steps recited may, in some instances, be performed in a different order; or equivalent structures and processes may be substituted for the structures and processes described. Since certain changes may be made in the above systems and methods without departing from the scope of the invention, it is intended that all subject matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in or inherently possessed by the systems, methods and compositions described in the claims below and by their equivalents.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US4021278||Dec 12, 1975||May 3, 1977||International Business Machines Corporation||Reduced meniscus-contained method of handling fluids in the manufacture of semiconductor wafers|
|US4102770 *||Jul 18, 1977||Jul 25, 1978||American Chemical And Refining Company Incorporated||Electroplating test cell|
|US5275690||Jun 17, 1992||Jan 4, 1994||Santa Barbara Research Center||Method and apparatus for wet chemical processing of semiconductor wafers and other objects|
|US5670034 *||Jun 17, 1996||Sep 23, 1997||American Plating Systems||Reciprocating anode electrolytic plating apparatus and method|
|US5938845 *||Oct 20, 1995||Aug 17, 1999||Aiwa Co., Ltd.||Uniform heat distribution apparatus and method for electroless nickel plating in fabrication of thin film head gaps|
|US6065424||Dec 18, 1996||May 23, 2000||Cornell Research Foundation, Inc.||Electroless deposition of metal films with spray processor|
|US6093453||May 17, 1999||Jul 25, 2000||Aiwa Co., Ltd.||Electroless plating method|
|US6165912||Sep 14, 1999||Dec 26, 2000||Cfmt, Inc.||Electroless metal deposition of electronic components in an enclosable vessel|
|US6431190||Sep 19, 2001||Aug 13, 2002||Kokusai Electric Co., Ltd.||Fluid processing apparatus|
|US6537416||Apr 25, 2000||Mar 25, 2003||Novellus Systems, Inc.||Wafer chuck for use in edge bevel removal of copper from silicon wafers|
|US6616772||Dec 3, 2002||Sep 9, 2003||Lam Research Corporation||Methods for wafer proximity cleaning and drying|
|US6632335||Dec 22, 2000||Oct 14, 2003||Ebara Corporation||Plating apparatus|
|US6660139 *||Nov 7, 2000||Dec 9, 2003||Ebara Corporation||Plating apparatus and method|
|US6689216 *||Aug 7, 2001||Feb 10, 2004||Ebara Corporation||Plating apparatus and plating liquid removing method|
|US6713122||Oct 15, 2002||Mar 30, 2004||Novellus Systems, Inc.||Methods and apparatus for airflow and heat management in electroless plating|
|US7166204 *||Jan 23, 2002||Jan 23, 2007||Ebara Corporation||Plating apparatus and method|
|US20030141018||Jan 28, 2002||Jul 31, 2003||Applied Materials, Inc.||Electroless deposition apparatus|
|WO2002059398A2 *||Jan 23, 2002||Aug 1, 2002||Ebara Corporation||Plating apparatus and method|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US7919332 *||Feb 27, 2004||Apr 5, 2011||Kitakyushu Foundation For The Advancement Of Industry Science And Technology||Biological molecule-immobilized chip and its use|
|US8147660||Mar 30, 2007||Apr 3, 2012||Novellus Systems, Inc.||Semiconductive counter electrode for electrolytic current distribution control|
|US8257781||Aug 11, 2005||Sep 4, 2012||Novellus Systems, Inc.||Electroless plating-liquid system|
|US8307779 *||Nov 9, 2009||Nov 13, 2012||Kabushiki Kaisha Toshiba||Coating apparatus|
|US8683942 *||Sep 24, 2010||Apr 1, 2014||Industrial Technology Research Institute||Chemical bath deposition apparatuses and fabrication methods for chemical compound thin films|
|US9139911 *||Feb 10, 2014||Sep 22, 2015||Industrial Technology Research Institute||Fabrication methods for chemical compound thin films|
|US9184060||Nov 14, 2014||Nov 10, 2015||Lam Research Corporation||Plated metal hard mask for vertical NAND hole etch|
|US20080096219 *||Feb 27, 2004||Apr 24, 2008||Tetsuya Haruyama||Biological Molecule-Immobilized Chip and Its Use|
|US20100116200 *||Nov 9, 2009||May 13, 2010||Ryouichi Takahashi||Coating apparatus|
|US20110318493 *||Sep 24, 2010||Dec 29, 2011||Industrial Technology Research Institute||Chemical bath deposition apparatuses and fabrication methods for chemical compound thin films|
|US20130302527 *||May 11, 2012||Nov 14, 2013||Shijan LI||Methods and apparatuses for electroless metal deposition|
|US20140161979 *||Feb 10, 2014||Jun 12, 2014||Industrial Technology Research Institute||Fabrication methods for chemical compound thin films|
|U.S. Classification||118/52, 118/731, 118/423, 118/429|
|Cooperative Classification||H01L21/288, H01L21/76841, H01L21/6715, C23C18/1619|
|European Classification||C23C18/16B6, H01L21/288|
|Aug 9, 2005||AS||Assignment|
Owner name: NOVELLUS SYSTEMS, INC.,CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:FENG, JINGBIN;MAYER, STEVEN T.;DINNEEN, DANIEL MARK;AND OTHERS;REEL/FRAME:016885/0212
Effective date: 20050801
|Oct 7, 2013||FPAY||Fee payment|
Year of fee payment: 4